1. Field of the Invention
This invention relates to an underlayer composition for silicon-containing photoresists, especially silicon-containing multilayer resists. More particularly, this invention relates to an underlayer composition that comprises a vinyl or acrylate polymer comprising a naphthalene moiety or naphthol moiety.
2. Description of the Related Art
In the microelectronics industry, there is a continued desire to reduce the size of structural features and/or to provide greater amount of circuitry for a given chip size. Advanced lithographic techniques are required to fabricate high performance and high density circuitry. Lithography impacts the manufacture of microscopic structures not only in terms of directly imaging patterns on the desired substrate, but also in terms of making masks typically used in such imaging.
The resolution capability of lithographic processes is generally a function of the wavelength of imaging radiation, the numerical aperture of the lens in the exposure tool and various resolution enhancing techniques used. Thinner resist also provides larger focus latitude and higher resolution. Thinning of a conventional single layer resist to improve resolution generally results in compromise of the etch resistance of the resist which is needed to transfer the desired image to the underlying material layer. In order to obtain the resolution enhancement benefit of thinner imaging layers, multilayer lithographic processes (e.g., bilayer processes) have been developed. In multilayer lithographic processes, a planarizing underlayer is used between the imaging resist layer (typically a silicon-containing resist) and the underlying material layer to be patterned by transfer from the patterned resist. The underlayer receives the pattern from the patterned resist layer, and then the patterned underlayer acts as a mask for the etching processes needed to transfer the pattern to the underlying material. Exemplary multilayer lithographic processes are described in U.S. Pat. Nos. 5,985,524, 6,444,408, 6,653,048, and U.S. Reissue Pat. No. RE38,282. These patents mention the use of polyacrylates as underlayers. U.S. Pat. No. 6,054,248 also discloses various polymers for use as underlayers.
While planarizing underlayer materials exist in the art, there is a continued desire for improved compositions, especially compositions useful in lithographic processes using imaging radiation having a wavelength less than 200 nm (e.g., 193 nm). Known underlayers for I-line and 248 nm DUV multilayer lithographic applications are typically based on novolac or polyhydroxystyrene polymers. For example, U.S. Pat. No. 6,340,734 discloses the use of diazonaphthoquinone (DNQ)/novolac or novolac resin as an underlayer material. These materials very strongly absorb 193 nm radiation, thus are not suitable for 193 nm lithographic applications.
The planarizing underlayer compositions should be sufficiently etchable with selectivity to the overlying photoresist (to yield a good profile in the etched underlayer) while being resistant to the etch process needed to pattern the underlying material layer. Additionally, the planarizing underlayer composition should have the desired optical characteristics (e.g., refractive index, optical density) such that the need for any additional antireflective layer is avoided. Examples of good refractive indexes for the underlayers are those that would provide the substrate reflectivity of about 1% or less. The planarizing underlayer composition should also have physical and chemical compatibility with the imaging resist layer to avoid unwanted interactions which may cause footing and/or scumming.
It is also desired to reduce the number of separate ingredients in the planarizing underlayer composition in order to enhance the economic viability of multilayer lithographic processes.
U.S. Pat. No. 6,818,381 describes compositions suitable for forming planarizing underlayers for multilayer lithographic processes, characterized by the presence of (A) a polymer containing: (i) cyclic ether moieties, (ii) saturated polycyclic moieties, and (iii) aromatic moieties for compositions not requiring a separate crosslinker, or (B) a polymer containing: (i) saturated polycyclic moieties, and (ii) aromatic moieties for compositions requiring a separate crosslinker. The compositions provide outstanding optical, mechanical and etch selectivity properties, and are especially useful in lithographic processes using radiation less than 200 nm in wavelength to configure underlying material layers. The teaching uses highly absorbing aromatic moieties which then can only be incorporated with small quantity in the polymer composition. One drawback of lower ratio of aromatic moieties is that the resulting polymer would have lower etch resistance for patterning the material layer under the underlayer. The other drawback is that it would be very difficult to get the right optical properties in the synthetic process, such as rendering the polymer either too high in absorption when too much aromatic moieties are incorporated, or too low in absorption when not enough aromatic moieties are incorporated.
U.S. Patent Application Pub. No. 2003/0073040A1 describes an underlayer film containing a polymer with a carbon content of 80 wt % or more. The polymer is an acenaphthylene polymer or its copolymer, which provides a very rigid composition. It is very difficult to tune the n and k values with this rigid composition.
Simple vinyl and acrylate polymers containing aromatic units with high etch resistance and good optical properties are needed for underlayers. There is also a need to have good underlayer composition for a trilayer resist structure.